The finding adds weight to the idea that methane being released from wetlands today may accelerate modern global warming.

Richard Pancost from Britain's University of Bristol and his colleagues studied the chemistry of 55-million-year-old sediments from the Cobham Lignite wetland in southeast England (see map of Britain).

By measuring the levels of organic compounds produced by bacteria, Pancost's team was able to estimate the levels of methane-eating microbes living in the bog in the distant past.

The researchers found a marked increase in a by-product left by methane-devouring microbes around 55 million years ago.
For the bacteria to have mushroomed so dramatically, Pancost and his colleagues suggest, methane emissions from the bog must have also radically increased.

The team's study will appear in tomorrow's issue of the journal Nature.

Runaway Warming

Warm, wet weather likely accelerated the rotting of plant material, which in turn triggered the methane burps from the Cobham Lignite bog, the researchers said.

Assuming that other wetlands responded in a similar way, such large amounts of methane could explain the extreme global warming seen at the time.

"If the increase in methane emissions were widespread, the increased methane flux from these settings could have amplified the warming occurring at this time," Pancost said.

Because methane is a key greenhouse gas, some scientists worry that a similar scenario today could trigger a runaway greenhouse effect. (Get the facts about global warming.)